1. Field of the Invention
The present invention relates to a circuit component including a flexible plate on which a barrier film and electrodes are formed, an electrode connection structure for connection between the electrodes and a display device including the electrode connection structure.
2. Description of the Related Art
For display devices such as liquid crystal displays, organic EL displays and electrophoretic displays, an active matrix substrate has widely been used as a first circuit component prepared by forming a plurality of thin film transistors (hereinafter referred to as TFTs) on a glass plate.
The TFTs are arranged in a matrix pattern. The active matrix substrate also carries thereon a plurality of source lines and gate lines arranged in a lattice pattern and connected to the TFTs. The source lines are arranged parallel to each other and the gate lines are arranged to be orthogonal to the source lines. The source and gate lines are extended such that their ends reach a frame region on the periphery of the substrate and terminals are formed at the ends (the terminals may be referred to as electrodes in the description).
A second circuit component such as an IC driver is implemented on the frame region. The IC driver includes a plurality of electrodes corresponding to the terminals. The electrodes of the IC driver are electrically connected to the terminals of the lines, respectively.
Press bonding using an anisotropic conductive film (ACF) is known as a method for electrically connecting the terminals of the first circuit component and the electrodes of the second circuit component. The ACF is an insulating adhesive material (binder) containing conductive particles dispersed therein. For example, it is prepared by dispersing conductive particles in an insulating thermosetting epoxy adhesive. The conductive particles may be particles made of nickel-gold plated cross linked polystyrene cores (see, for example, Japanese Unexamined Patent Publication No. 9-199206).
In recent years, the above-listed displays are demanded to be portable and flexible. With this trend, research has been conducted to use a lightweight and flexible plastic plate as the active matrix substrate in place of the glass plate.
In general, the plastic plate is much more likely to absorb moisture than the glass plate. Therefore, the plate is apt to shrink or warp. For this reason, a barrier film such as an impervious inorganic film is stacked on the surface of the plastic plate. That is, if the plastic plate is used for the active matrix substrate (first circuit component), the lines and terminals are formed on the barrier film stacked on the plastic plate.
If the IC driver (second circuit component) is implemented on the active matrix substrate (first circuit component) using the plastic plate by press bonding, pressure is concentrated on the terminals on the relatively soft plastic plate. Therefore, a crack is likely to occur in the barrier film below the terminals. This phenomenon occurs significantly when the ACF containing the conductive particles is used.
Referring to FIG. 27 and FIG. 28, a conventional electrode connection structure will be explained. FIG. 27 is an enlarged sectional view illustrating the connection structure and FIG. 28 is a plan view illustrating an enlargement of a cracked part of the first circuit component.
A TFT substrate 101 as the first circuit component includes a plastic plate 102, a barrier film 103 stacked on the plastic plate 102, such as an inorganic film, and a plurality of terminals 104 as first electrodes formed on the surface of the barrier film 103. The terminals 104 are arranged at predetermined intervals and adjacent to each other. Though not shown, a circuit section including lines and electrodes is also formed on the barrier film 103 of the TFT substrate 101.
An IC driver 105 as the second circuit component includes A plurality of bumps 106 as second electrodes. An anisotropic conductive film 107 is provided between the IC driver 105 and the TFT substrate 101 to surround the bumps 106 and the terminals 104. As the IC driver 105 is implemented on the TFT substrate 101 by press bonding, the bumps 106 are electrically connected to the terminals 104.
When the terminal 104 is damaged and a crack 110 is generated in a portion of the barrier film 103 below the damaged terminal, the crack 110 grows and expands in the barrier film 103. As a result, the other terminals 104b adjacent to the first damaged terminal 104a and the circuit section such as lines (not shown) are damaged or broken by the crack 110 propagated in the barrier film 103. In such a case, display quality of the display device including the TFT substrate 101 is decreased.
According to a known technique for solving such a problem, a breaking stress of the plating on the conductive particles is set relatively low (e.g., 73 MPa or lower) and the press bonding stress is set higher than the breaking stress of the plating (See, for example, Japanese Unexamined Patent Publication No. 2001-337340). The technique is intended to keep the electrical connection excellent by reducing the damage to the terminals.
If the material of the terminals and the size and material of the conductive particles are varied, the technique of Japanese Unexamined Patent Publication No. 2001-337340 may not work enough to reduce the damage to the terminals of the first circuit component caused in the press bonding of the second circuit component and the electrical connection may not be maintained in good condition.
The problem also arises in the cases where the ACF is not provided (i.e., the terminals are directly press bonded), where the ACF is replaced with conductive paste, an NCF (non conductive film) or an adhesive resin, and where common transfer electrodes are interposed between the electrodes.
Further, due to low adhesion of the barrier film to the plastic plate, there is also a problem of low adhesion of the second circuit component to the plastic plate of the first circuit component.